Positive electrode active material for lithium secondary battery, manufacturing method for the same, and lithium secondary battery including the same

Abstract

To provide a positive electrode active material having the battery characteristics in which low temperature capacity, average voltage, energy density, and lifetime are improved, in which the adhesive power with a current collector is also high, a manufacturing method for the same, and a lithium secondary battery.SOLUTION: A positive electrode active material for a lithium secondary battery includes a first particle containing a compound expressed by the following chemical formula 1 and having a first average particle diameter and a second particle containing a compound expressed by the following chemical formula 2 and having a second average particle diameter that is larger than the first average particle diameter. Each of the first particle and the second particle is in a spherical secondary particle form, and the content amount of the first particle is more than or equal to that of the second particle. [Chemical Formula 1] Lia1Mnw1Fex1Tiy1B1z1 PO4-b1, and [Chemical Formula 2] Lia2Fex2Tiy2B2z2 PO4-b2. Each of B1 in Chemical Formula 1 and B2 in Chemical Formula 2 is at least one element selected from the group consisting of transition metals with an oxidation number of 4.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, and more particularly to a positive electrode active material including an olivine-based lithium compound, a manufacturing method thereof, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid replenishment of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively carried out.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated from the cathode and the anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent Publication No. 2014-0068893 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material that has battery characteristics such as improved low-temperature capacity, average voltage, energy density, and lifespan, and also has high adhesive strength with the current collector.

[0006] Another object of the present invention is to provide a lithium secondary battery having improved battery characteristics such as low-temperature capacity, average voltage, energy density, and lifespan, and also having high adhesion to a current collector. [Means for solving the problem]

[0007] A cathode active material according to the present invention may include first particles having a first average particle size, the first particles including a compound represented by the following Chemical Formula 1, and second particles having a particle size larger than the first average particle size, the second particles including a compound represented by the following Chemical Formula 2. The content of the first particles may be equal to or greater than the content of the second particles. [Chemical formula 1] Li a1 Mn w1 Fe x1 Ti y1 B1 z1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦w1≦0.7, 0.3≦x1≦0.7, 0≦y1≦0.05, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1+w1=1 may be satisfied. [Chemical formula 2] Li a2 Fe x2 Ti y2 B2 z2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.900≦x2≦0.999, 0.001≦y2≦0.05, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1.

[0008] B1 in Formula 1 and B2 in Formula 2 may each be at least one element selected from the group consisting of transition metals having an oxidation number of 4.

[0009] According to another aspect of the present invention, a method for manufacturing a positive electrode active material may include: manufacturing first particles having a first average particle size; manufacturing second particles having a second average particle size larger than the first average particle size; and mixing the first particles and the second particles at a mixing ratio of 50:50 to 99:1.

[0010] Producing the first particles can include: mixing a manganese iron phosphate precursor, a first lithium source, a first carbon source, and a first titanium source to form a first mixture, drying the first mixture by spray drying, and calcining the dried first mixture. Producing the second particles can include mixing an iron phosphate precursor, a second lithium source, a second carbon source, and a second titanium source to form a second mixture, drying the second mixture by spray drying, and calcining the dried second mixture.

[0011] A lithium secondary battery according to yet another aspect of the present invention may include the above-described positive electrode active material. [Effects of the Invention]

[0012] The positive electrode active material according to the present invention may include first particles, which are secondary particles, and second particles, which are secondary particles, thereby providing battery characteristics such as improved low-temperature capacity, average voltage, energy density, and lifespan, and also increasing adhesion to the current collector.

[0013] The lithium secondary battery according to the present invention can have improved battery characteristics such as low-temperature capacity, average voltage, energy density, and lifespan, and can also have high adhesion to the current collector. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a cylindrical battery configuration. [Figure 3] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a prismatic battery shape. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which can be said to have a pouch-type battery configuration. [Figure 6] 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. FIG. [Figure 7] 1 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. [Figure 8] FIG. 2 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to Comparative Example 1 of the present invention. [Figure 9a] 1 is an SEM image of the positive electrode active material of Example 1 of the present invention. [Figure 9b] 1 is an SEM image of the positive electrode active material of Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. However, the description of the present embodiments is provided to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0016] In this specification, when a component is referred to as being on another component, it means that it may be formed directly on the other component, or that a third component may be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated to effectively explain the technical content. Parts designated with the same reference numerals throughout this specification refer to the same components.

[0017] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0018] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0019] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0020] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0021] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0022] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0023] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIG. 6. The current collector COL1 may be made of, but is not limited to, aluminum.

[0024] negative electrode 20 The lithium secondary battery positive electrode 20 may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0025] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0026] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0027] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0028] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0029] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound to impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0030] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0031] The conductive material is used to impart conductivity to the electrode and may be any material that does not cause chemical changes in the constructed battery and is electronically conductive. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0032] The current collector COL2 may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0033] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, a lithium metal alloy, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0034] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0035] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0036] As a substance that can be doped or undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0037] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it can include secondary particles (cores) combined with primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0038] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0039] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0040] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, but it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0041] Separator 30 may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0042] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0043] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0044] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0045] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be stacked.

[0046] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0047] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0048] The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0049] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0050] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0051] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of non-quantum solvents that can be used include nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0052] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0053] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain cyclic carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0054] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0055] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 2 illustrating a cylindrical battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch battery types. Referring to FIGS. 2 to 5, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the positive electrode assembly 40 to the outside.

[0056] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0057] FIG. 6 is an enlarged view of a positive electrode active material layer of a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 6, as described above, the positive electrode active material layer AML1 (see FIG. 1) may include first particles PTC1, second particles PTC2, a conductive material CDM, and a binder BND. The first particles PTC1 may be spherical or elliptical secondary particles formed by agglomerating at least two or more first primary particles NNP1. The second particles PTC2 may be spherical or elliptical secondary particles formed by agglomerating at least two or more second primary particles NNP2. A plurality of first particles PTC1 and a plurality of second particles PTC2 may constitute a positive electrode active material according to an embodiment of the present invention.

[0058] The positive electrode active material layer AML1 may further contain an additive that can function as a sacrificial positive electrode.

[0059] The content of the positive electrode active materials PTC1 and PTC2 in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1. The content of the binder BND and the conductive material CDM may be 0.5 wt % to 5 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0060] The binder BND can bind the first particles PTC1, the second particles PTC2, and the conductive material CDM to one another. As an example, the binder BND can include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but is not limited thereto.

[0061] The conductive material CDM can be used to improve the conductivity of the positive electrode active material layer AML1. Any conductive material that does not cause a chemical change in the positive electrode active material layer AML1 can be used as the conductive material CDM. For example, the conductive material CDM can include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0062] The first particles PTC1 and the second particles PTC2 will be described in more detail below.

[0063] 1st particle PTC1 The first particles PTC1 may be polycrystalline and may be secondary particles formed by agglomerating at least two or more first primary particles NNP1. In other words, one first particle PTC1 may include a plurality of first primary particles NNP1 agglomerated together. The first particles PTC1 may have a spherical or elliptical shape.

[0064] As an example, the first particles PTC1 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the first particles PTC1 or may cover a portion of the surface of the first particles PTC1. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability of the first particles PTC1 and thereby improve electrical conductivity.

[0065] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a transition metal-containing compound having an oxidation number of 4. Metal-containing compounds such as titanium-containing compounds and transition metal-containing compounds having an oxidation number of 4 may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compound may further include other metal or non-metal elements. For example, the metal-containing compound may further include lithium.

[0066] As an example, the first particle PTC1 may further include a grain boundary coating layer on the surface of each of the first primary particles NNP1. The grain boundary coating layer may be present inside the first particle PTC1. The grain boundary coating layer may be formed by coating along the interface between the first primary particles NNP1 inside the first particle PTC1. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the first particle PTC1. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a transition metal-containing compound having an oxidation number of 4.

[0067] The interior of the first particle PTC1 described above may refer to the entire interior of the first particle PTC1 excluding the surface of the first particle PTC1. For example, the interior of the first particle PTC1 may refer to the region from a depth of about 10 nm from the surface of the first particle PTC1 to the entire inside, or from a depth of 10 nm to a depth of about 2 μm.

[0068] The first particles PTC1 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the first particles PTC1. In addition, the first particles PTC1 further include a grain boundary coating portion, which further improves the electrical conductivity of the first particles PTC1.

[0069] The average particle size of the first particles PTC1 may be 1 μm to 15 μm, 1 μm to 10 μm, or 3 μm to 7 μm. The average particle size of the first particles PTC1 may be substantially the same as or smaller than the average particle size of the second particles PTC2 described below. In one example, the average particle size of the first particles PTC1 may be measured using a particle size analyzer, and the diameter of particles whose cumulative volume is 50% by volume (D50) in the particle size distribution may be defined as the average particle size.

[0070] The size of the first primary particles NNP1 of the first particles PTC1 may be 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm. The size of the first primary particles NNP1 of the first particles PTC1 may be smaller than the size of the second primary particles NNP2 of the second particles PTC2 described below. In one embodiment, the measurement of the size of the first primary particles NNP1 may refer to the diameter measured by randomly selecting approximately 30 first primary particles NNP1 from an electron microscope photograph of the positive electrode active material. The size of the first primary particles NNP1 may be uniform.

[0071] The first particles PTC1 may include an olivine-based lithium compound represented by the following Chemical Formula 1.

[0072] [Chemical formula 1] Li a1 Mn w1 Fe x1 Ti y1 B1 z1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦w1≦0.7, 0.3≦x1≦0.7, 0≦y1≦0.05, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1+w1=1. B1 in Chemical Formula 1 may be at least one element selected from the group consisting of transition metals having an oxidation number of 4.

[0073] The Ti contained in the first particles PTC1 can have the effect of controlling the growth of the first primary particles NNP1 of the first particles PTC1, thereby making the size of the first primary particles NNP1 of the first particles PTC1 more uniform and smaller. In one embodiment, the Ti doping amount of the first particles PTC1 can be 1,000 ppm to 3,000 ppm, or 1,500 ppm to 3,000 ppm. Alternatively, the Ti doping amount of the first particles PTC1 can be defined as the weight of Ti relative to the total metal weight excluding lithium from the olivine-based lithium active material represented by Chemical Formula 1. For example, LiMn 0.6 Fe 0.396 Ti 0.004In the case of PO4, the Ti doping amount can be about 2,000 ppm. When the Ti content satisfies the doping range, the first primary particles NNP1 of the first primary particles PTC1 can be produced to the size targeted by the present invention.

[0074] The first particles PTC1 may further contain carbon derived from the coating layer and / or the grain boundary coating layer. The carbon element content in the first particles PTC1 may be 0.5 wt% to 10 wt%, 1 wt% to 3 wt%, or 1.5 wt% to 2.0 wt%. The carbon element content of the first particles PTC1 may be greater than the carbon element content of the second particles PTC2.

[0075] The first particles PTC1 may have a spherical shape formed by the aggregation of nano-sized first primary particles NNP1. The first particles PTC1 may exhibit the following characteristics due to the close aggregation of the first primary particles NNP1: The first particles PTC1 may have a spherical or elliptical shape. The average particle size (D50) of the first particles PTC1 may be 1 μm to 7 μm. The porosity of the first particles PTC1 may be about 15% to about 40%, or about 30% to 40%. The Span value of the first particles PTC1 analyzed with a particle size analyzer may be 0.3 to 0.75. The porosity of the first particles PTC1 may be greater than the porosity of the second particles PTC2.

[0076] When the first particles PTC1 are in the form of spherical secondary particles formed by agglomeration of nano-sized first primary particles NNP1, the amount of binder BND required to attach the first particles PTC1 to the current collector COL1 (see FIG. 1) may be relatively smaller than when the first particles PTC1 are in the form of single particles. This may be because the first particles PTC1 have a secondary particle form, which increases the average particle size compared to when they are in the form of single particles, thereby increasing the adhesive strength with the current collector COL1.

[0077] The term "single particle" as used above may refer to a single particle without an internal grain boundary. The term "single particle" may refer to a morphologically distinct particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are not aggregated with each other and exist in an independent phase. For example, the single particle may be a single crystal. Alternatively, the single particle may be a particle containing several crystals. The single particle may be in a singly isolated form. Alternatively, the single particle may be in a form in which 2 to 100 single particles are attached to each other. Alternatively, the single particle may be in an amorphous form in which multiple single particles are randomly aggregated. The diameter of the single particle may vary. For example, when the first particle PTC1 is in a single particle form, the first average particle diameter may be 0.2 μm to 2.5 μm.

[0078] 2nd particle PTC2 The second particles PTC2 may have a polycrystalline form and may include secondary particles formed by agglomeration of at least two or more second primary particles NNP2. In other words, one second particle PTC2 may include a plurality of second primary particles NNP2 agglomerated together. The second particles PTC2 may have a spherical or elliptical shape.

[0079] As an example, the second particles PTC2 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the second particles PTC2 or may cover only a portion of the surface of the second particles PTC2. For example, the coating layer may include carbon and / or a carbon-containing compound.

[0080] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a transition metal-containing compound having an oxidation number of 4. Metal-containing compounds such as titanium-containing compounds and transition metal-containing compounds having an oxidation number of 4 may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compound may further include other metal or non-metal elements. For example, the metal-containing compound may further include lithium. The coating layer may improve the structural stability of the second particles PTC2, thereby improving electrical conductivity.

[0081] As an example, the second particle PTC2 may further include a grain boundary coating layer on the surface of each of the second primary particles NNP2. The grain boundary coating layer may be present inside the second particle PTC2. The grain boundary coating layer may be formed by coating along the interface between the second primary particles NNP2 inside the second particle PTC2. In other words, the grain boundary coating layer may refer to a material coated on the grain boundaries inside the second particle PTC2. The grain boundary coating layer may include carbon and / or a carbon-containing compound. The grain boundary coating layer may further include at least one selected from the group consisting of a titanium-containing compound and a transition metal-containing compound having an oxidation number of 4.

[0082] The interior of the second particle PTC2 described above can refer to the entire interior of the second particle PTC2 excluding the surface of the second particle PTC2. For example, the interior of the second particle PTC2 can refer to the region from a depth of about 10 nm from the surface of the second particle PTC2 to the entire inside, or from a depth of 10 nm to a depth of about 2 μm.

[0083] The second particles PTC2 further include a grain boundary coating portion, which enhances structural stability and allows a uniform coating layer to be formed on the surface of the second particles PTC2. In addition, the second particles PTC2 further include a grain boundary coating portion, which further improves the electrical conductivity of the second particles PTC2.

[0084] The average particle size of the second particles PTC2 may be 2 μm to 15 μm, 3 μm to 12 μm, or 3 μm to 10 μm. For example, the second average particle size of the second particles PTC2 may be approximately 5 μm. The average particle size of the second particles PTC2 may be substantially the same as or larger than the average particle size of the first particles PTC1. In one example, the average particle size of the second particles PTC2 may be measured using a particle size analyzer, and the diameter of the particles whose cumulative volume is 50% by volume (D50) in the particle size distribution may be defined as the average particle size.

[0085] The size of the second primary particles NNP2 of the second particles PTC2 may be 50 nm to 300 nm, 100 nm to 300 nm, or 200 nm to 300 nm. The size of the second primary particles NNP2 of the second particles PTC2 may be larger than the size of the first primary particles NNP1 of the first particles PTC1. In one embodiment, the size of the second primary particles NNP2 may be measured by randomly selecting approximately 30 second primary particles NNP2 from an electron microscope photograph of the positive electrode active material. The size of the second primary particles NNP2 may be uniform.

[0086] The second particles PTC2 may include an olivine-based lithium compound represented by Chemical Formula 2.

[0087] [Chemical formula 2] Li a2 Fe x2 Ti y2 B2 z2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.900≦x2≦0.999, 0.001≦y2≦0.05, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1, and in Chemical Formula 2, B2 is at least one element selected from the group consisting of transition metals having an oxidation state of 4.

[0088] The Ti contained in the second particles PTC2 can have the effect of controlling the growth of the second primary particles NNP2 of the second particles PTC2, thereby making the size of the second primary particles NNP2 of the second particles PTC2 more uniform and smaller. In one example, the Ti doping amount of the second particles PTC2 can be 1,000 ppm to 3,000 ppm, or 500 ppm to 1,500 ppm. When the Ti content falls within the doping range, the second primary particles NNP2 of the second primary particles PTC2 can be produced to the size desired by the present invention.

[0089] According to an embodiment of the present invention, the doping amount (or content) of Ti in the first particle PTC1 may be greater than the doping amount (or content) of Ti in the second particle PTC2, and thus the size of the first primary particles NNP1 of the first particle PTC1 may be smaller than the size of the second primary particles NNP2 of the second particle PTC2.

[0090] The second particles PTC2 may further contain carbon derived from the coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1 wt % to 1.9 wt %.

[0091] The second particles PTC2 may have a spherical shape formed by the aggregation of nano-sized second primary particles NNP2. The second particles PTC2 may exhibit the following characteristics due to the close aggregation of the second primary particles NNP2: The second particles PTC2 may have a spherical or elliptical shape; The average particle size (D50) of the second particles PTC2 may be 3 μm to 10 μm; The porosity of the second particles PTC2 may be about 15% to about 30%, or about 20% to 30%; The Span value of the second particles PTC2 analyzed with a particle size analyzer may be 0.3 to 0.75.

[0092] According to an embodiment of the present invention, the size of the first primary particles NNP1 of the first particles PTC1 may be smaller than the size of the second primary particles NNP2 of the second particles PTC2. Nevertheless, the porosity of the first particles PTC1 may be larger than the porosity of the second particles PTC2. This may be due to the fact that the adhesive force between the first primary particles NNP1 is relatively reduced due to the small size of the first primary particles NNP1 of the first particles PTC1.

[0093] When the second particles PTC2 are in the form of spherical secondary particles formed by agglomeration of nano-sized second primary particles NNP2, the amount of binder BND required to attach the second particles PTC2 to the current collector COL1 (see FIG. 1) may be relatively smaller than when the second particles PTC2 are in the form of single particles. This may be because the second particles PTC2 have a secondary particle form, which increases the average particle size compared to when the second particles PTC2 are in the form of single particles, thereby increasing the adhesive strength with the current collector COL1.

[0094] Furthermore, when the second particles PTC2 are in the form of spherical secondary particles formed by agglomeration of nano-sized second primary particles NNP2, the amount of binder BND required to attach the second particles PTC2 to the current collector COL1 (see FIG. 1) may be relatively smaller than that of the first particles PTC1, which are in the form of spherical secondary particles formed by agglomeration of nano-sized first primary particles NNP1. This may be due to the fact that the average particle size of the second particles PTC2 is relatively larger than that of the first particles PTC1.

[0095] In one embodiment, the cathode active material of the present invention may include a specific mixture of primary particles PTC1 and secondary particles PTC2 in the form of secondary particles. This allows the cathode active material to have the advantages of the primary particles PTC1, such as high low-temperature capacity, high average voltage, high energy density, and long lifespan, while also having the advantages of the secondary particles PTC2, such as high adhesive strength to the current collector COL1 (see FIG. 1). In other words, compared to a cathode active material composed solely of primary particles PTC1, the cathode active material may have improved battery characteristics that are the same or similar to those of the primary particles PTC1, and the cathode manufacturing process may be relatively easy.

[0096] Referring again to Figure 6, a cathode active material according to an embodiment of the present invention will be described in more detail. The cathode active material of the present invention may include first particles PTC1 and second particles PTC2. The mixture ratio of the first particles PTC1 to the second particles PTC2 in the cathode active material may be 50:50 to 99:1.

[0097] In one embodiment, the mixing ratio of the first particles PTC1 and the second particles PTC2 may be adjusted so that the content of Mn in the metal elements excluding lithium in the positive electrode active material is 25 at % to 70 at %. For example, when the first particles PTC1 are LiMn 0.6 Fe 0.4 When the first particle PTC1 contains LiFePO4 and the second particle PTC2 contains LiFePO4, the mixture ratio of the first particle PTC1 and the second particle PTC2 can be adjusted to about 70:30. In this case, the Mn content of the metal elements excluding lithium in the mixture can be about 42 at%.

[0098] Since the first particles PTC1 contain Mn, the operating voltage and energy density of the secondary battery can be improved compared to the second particles PTC2. The cathode active material according to this embodiment can improve the operating voltage compared to a typical LFP battery by mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio and adjusting the Mn content to 25 at% to 70 at%. In one embodiment, the average voltage of the lithium secondary battery of the present invention can be 3.0 V to 4.5 V. Meanwhile, since the average voltage is proportional to the energy density, the increase in the average voltage can also contribute to an increase in the energy density.

[0099] The cathode active material of the present invention can improve the composite density, capacity, and lifespan by mixing the first secondary particle PTC1 and the second secondary particle PTC2. In one embodiment, the composite density of the cathode active material of the present invention may be 2.0 g / cc to 2.5 g / cc.

[0100] The cathode active material of the present invention can improve low-temperature characteristics by mixing first particles PTC1, which are secondary particles, with second particles PTC2, which are single particles. In one example, the capacity at −20° C. relative to the initial discharge amount at 25° C. of the lithium secondary battery (capacity at −20° C. / initial discharge amount at 25° C.) may be 75% or more. For example, the capacity at −20° C. relative to the initial discharge amount at 25° C. of the lithium secondary battery of the present invention (capacity at −20° C. / initial discharge amount at 25° C.) may be 30% to 90%, 50% to 90%, or 75% to 90%.

[0101] Method for producing positive electrode active material 7 is a flowchart illustrating a method for manufacturing a positive electrode active material according to an embodiment of the present invention. The method for manufacturing the first particles PTC1 according to an embodiment of the present invention will be described in more detail with reference to FIG.

[0102] A manganese iron phosphate precursor, a lithium source, a carbon source, and a titanium source can be mixed in a solvent (S100). For example, the solvent can be water, ethanol, or the like. The manganese iron phosphate precursor can be a compound containing all of manganese (Mn), iron (Fe), and phosphorus (P); a mixture of a manganese (Mn)-containing compound and a compound containing iron (Fe) and phosphorus (P); or a mixture of a manganese (Mn)-containing compound, an iron (Fe)-containing compound, and a phosphorus (P)-containing compound. For example, the manganese iron phosphate precursor can be a compound containing Mn x Fe 1-x PO4·H2O; a mixture of MnCO3 and FePO4·H2O; or a mixture of MnCO3, FeSO4 and H3PO4, where x can be 0.3 to 0.7.

[0103] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0104] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0105] The titanium source can include an oxide containing titanium metal and / or a chloride containing titanium metal. For example, the titanium source can be titanium oxide.

[0106] The mixture may be subjected to wet milling (S200). A typical wet mill capable of controlling the temperature may be used for wet milling. Specifically, at least one selected from a bead mill, a ball mill, an attrition mill, an apex mill, a super mill, and a basket mill may be used for wet milling. Through the wet milling process, particles in the mixture may be milled to a fine size.

[0107] In one embodiment of the present invention, the wet-milling step (S200) may be omitted. Specifically, in order to maximize the average particle size of the first particles PTC1 that are finally produced, the wet-milling step (S200) of the precursor particles may be omitted.

[0108] A dried mixture can be formed by removing the solvent from the mixture. In one embodiment of the present invention, forming the dried mixture can include spray drying the mixture (S300). The spray drying can be performed using commonly used spray drying equipment. For example, the spray drying can be performed using at least one selected from an ultrasonic spray dryer, an air nozzle spray dryer, an ultrasonic nozzle spray dryer, a filter expansion droplet generator, and an electrostatic spray dryer.

[0109] The particles refined to the size of primary particles through the wet grinding process can be agglomerated together through the spray drying process to form secondary particles. Therefore, the primary particles PTC1 can be formed in the form of secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0110] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), expressed as a percentage. As an example, the spray liquid may have a solid content of approximately 30% by weight.

[0111] If the solid content is less than 20%, the average particle size of the first particles PTC1 may become small, which may result in problems such as low productivity, whereas if the solid content is more than 40%, it may become difficult to control the average particle size of the first particles PTC1, which may result in large size deviations of the first particles PTC1.

[0112] The spray liquid according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at a solids content. For example, the spray liquid may have a viscosity of about 2000 mPa·s.

[0113] In one example, spray drying can be performed at a temperature of 100°C to 300°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0114] The spray flow rate for spray drying can be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is more than 80 ml / min, the mixture may not be completely dried due to water condensation in the spray dryer.

[0115] The spray liquid may be supplied at a pressure of 0.3 MPa to 0.7 MPa. For example, the spray liquid may be supplied at a pressure of about 0.5 MPa.

[0116] The dried mixture may be calcined under an inert atmosphere (S400). The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The temperature of the calcination process may be 500°C to 1000°C, or 600°C to 800°C. The calcination process may be performed for 4 hours to 20 hours, or 6 hours to 12 hours. By calcining the dried mixture, first particles PTC1 containing the compound of Formula 1 may be formed.

[0117] The sintered first particles PTC1 may be subjected to a dry-pulverization process (S500). The sintered mixture may be pulverized using an air jet mill or the like. The rotation speed of the dry-pulverization may be 5,000 rpm to 7,000 rpm. When dry-pulverization is performed within this rotation speed range, the first particles PTC1 may have a secondary particle form. The dry-pulverization process for the first particles PTC1 may be omitted.

[0118] The method for manufacturing first particles PTC1 according to the present invention can uniformly form a carbon coating layer on the surface of first primary particles NNP1 by introducing a carbon source into a manganese iron phosphate precursor. The first primary particles NNP1 can then be closely agglomerated through spray drying to form dense secondary spherical particles. As a result, the first particles PTC1 can include stable carbon coating layers on both the exterior and interior of the first particles PTC1, thereby having a relatively high carbon content. The high carbon content of the first particles PTC1 can improve the conductivity of the positive electrode active material layer AML1.

[0119] The method for producing the second particles PTC2 according to the embodiment of the present invention will be described in more detail.

[0120] The iron phosphate precursor, lithium source, carbon source, and titanium source can be mixed in a solvent (S100). For example, the solvent can be water, ethanol, or the like. The iron phosphate precursor can be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor can include FePO4·H2O or a mixture of FeSO4 and H3PO4. The lithium source, carbon source, and titanium source may be the same as or similar to those in the method for producing the first particles PTC1 described above.

[0121] The mixture may be subjected to wet-milling (S200). The wet-milling process may be the same as or similar to the method for producing the first particles PTC1 described above.

[0122] In one embodiment of the present invention, the wet-milling step (S200) may be omitted. Specifically, in order to maximize the average particle size of the second particles PTC2 to be finally produced, the wet-milling step (S200) of the precursor particles may be omitted.

[0123] The solvent may be removed from the mixture to form a dried mixture. In one embodiment of the present invention, forming the dried mixture may include spray drying the mixture (S300). The spray drying equipment may be the same as or similar to the spray drying equipment for the first particles PTC1 described above.

[0124] The particles refined to the size of primary particles through the wet milling process can be agglomerated together through the spray drying process to form secondary particles. Therefore, the secondary particles PTC2 can be formed in the form of secondary particles of a desired size by adjusting the flow rate and velocity of the carrier gas, temperature, residence time in the reactor, and internal pressure during the spray drying process.

[0125] As an example, the mixture to be spray-dried may have a total solid content of 20% to 40%. The solid content may refer to the weight of the solid material (i.e., the dried mixture) remaining after the solvent has evaporated relative to the total weight of the mixture (i.e., the spray liquid), expressed as a percentage. As an example, the spray liquid may have a solid content of approximately 30% by weight.

[0126] If the solid content is less than 20%, the average particle size of the second particles PTC2 will be small, which may result in problems such as low productivity.If the solid content is more than 40%, it will be difficult to control the average particle size of the second particles PTC2, and the size deviation of the second particles PTC2 may be large.

[0127] The spray liquid according to this embodiment may have a viscosity of 1500 mPa·s to 2500 mPa·s at a solids content. For example, the spray liquid may have a viscosity of about 2000 mPa·s. In one example, spray drying can be performed at a temperature of 100°C to 300°C. The propellant gas (e.g., air) used in spray drying can be introduced at a first temperature and discharged at a second temperature. For example, the first temperature can be 200°C to 250°C. The second temperature can be 80°C to 150°C.

[0128] The flow rate of the spray liquid for spray drying can be 30 ml / min to 80 ml / min. If the flow rate is less than 30 ml / min, problems such as nozzle clogging and reduced productivity may occur. If the flow rate is more than 80 ml / min, the mixture may not be completely dried due to water condensation in the spray dryer.

[0129] The spray liquid may be supplied at a pressure of 0.3 MPa to 0.7 MPa. For example, the spray liquid may be supplied at a pressure of about 0.5 MPa.

[0130] The dried mixture can be calcined under an inert atmosphere (S400). The calcination process may be the same as or similar to the method for producing the first particles PTC1 described above.

[0131] The sintered second particles PTC2 may be subjected to a dry pulverization process (S500). The sintered mixture may be pulverized using an air jet mill or the like. The rotation speed of the dry pulverization may be 0 rpm to 7,000 rpm. When dry pulverization is performed within this rotation speed range, the second particles PTC2 may have a secondary particle form. The dry pulverization process for the second particles PTC2 may be omitted.

[0132] The method for producing second particles PTC2 according to the present invention can uniformly form a carbon coating layer on the surface of second primary particles NNP2 by introducing a carbon source into an iron phosphate precursor. The second primary particles NNP2 are then closely aggregated through spray drying to form dense secondary spherical particles. As a result, the second particles PTC2 can include stable carbon coating layers on both the exterior and interior of the second particles PTC2, thereby having a relatively high carbon content. The high carbon content of the second particles PTC2 can improve the conductivity of the positive electrode active material layer AML2.

[0133] The prepared first particles PTC1 and second particles PTC2 are mixed in an appropriate ratio to form a positive electrode active material according to an embodiment of the present invention.

[0134] Carbon elemental analysis according to an embodiment of the present invention can be performed using an Elementar Micro Cube elemental analyzer. Specific operating methods and conditions are as follows: 1-2 mg of sample is weighed into a tin cup, placed on an automatic sampling tray, and introduced into a combustion tube through a ball valve. The sample is then burned at a combustion temperature of 1000°C. The burned gas is then reduced using reduced copper to form carbon dioxide. Carbon dioxide is detected using a TCD detector.

[0135] According to an embodiment of the present invention, the carbon content is measured by quantitative analysis of the particle surface using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Other methods for measuring the carbon content include inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0136] Examples of the present invention and comparative examples are described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0137] Comparative Example 1: Preparation of single particle first particles Mn 0.6 Fe 0.4 Manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.004. 10 wt% glucose was added to the mixture. The mixture was wet-pulverized using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined product was pulverized at a rotation speed of 8,000 rpm to obtain primary particles in the form of single particles. The average particle size of the primary particles was 100nm to 200nm. The Ti doping amount was 2,000ppm.

[0138] Comparative Example 2: Preparation of second particles in the form of single particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.002. The secondary particles were prepared in the same manner as in Comparative Example 1, except that 10 wt% glucose was added to the mixture. The average particle size of the primary particles of the secondary particles was 200 nm to 300 nm. The doping amount of Ti was 1,000 ppm.

[0139] Example 1: Preparation of primary particles in the form of secondary particles Mn 0.6 Fe 0.4 Manganese iron phosphate precursor (PO4), lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.004. 12 wt% glucose was added to the mixture. The slurry mixture was spray-dried at a spray pressure of 0.5 MPa and a temperature of 230°C, followed by evaporation. The dried mixture was calcined at 750°C for 10 hours in a nitrogen atmosphere to obtain primary particles in the form of secondary particles. The average particle size of the primary particles of the primary particles was 50 nm to 200 nm. The doping amount of Ti was 2,000 ppm.

[0140] Example 2: Preparation of secondary particles Iron phosphate precursor Fe1PO4, lithium carbonate, and titanium dioxide were mixed in a molar ratio of Fe:Li:Ti = 1:1.03:0.002. The secondary particles were prepared in the same manner as in Example 1, except that 10 wt% glucose was added to the mixture. The average particle size of the primary particles of the secondary particles was 200 nm to 300 nm. The doping amount of Ti was 1,000 ppm.

[0141] Example 3-1: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 30:70 to prepare a positive electrode active material.

[0142] Example 3-2: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 40:60 to prepare a positive electrode active material.

[0143] Example 3-3: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 50:50 to prepare a positive electrode active material.

[0144] Example 3-4: Preparation of a mixture of first particles and second particles The first particles of Example 1 and the second particles of Example 2 were mixed in a mass ratio of 60:40 to prepare a positive electrode active material.

[0145] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0146] Lithium secondary battery manufacturing A 2032-type coin-shaped half cell was fabricated using the prepared positive electrode and a lithium metal counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0147] Evaluation example 1: Analysis of the surface of the positive electrode active material An SEM image of the positive electrode active material prepared in Example 1 is shown in Figure 9a. An SEM image of the positive electrode active material prepared in Example 2 is shown in Figure 9b. Referring to Figure 9a, it can be seen that the first particles according to an embodiment of the present invention are in the form of spherical secondary particles formed by agglomeration of a plurality of first primary particles. Referring to Figure 9b, it can be seen that the second particles according to an embodiment of the present invention are in the form of spherical secondary particles formed by agglomeration of a plurality of second primary particles.

[0148] Evaluation Example 2: Active Material Evaluation I The pellet density (PD) and carbon content of the positive electrode active materials of Comparative Examples 1 and 2 and Examples 1 and 2 were measured, and the results are shown in Table 1.

[0149] [Table 1]

[0150] Referring to Table 1, it can be seen that the cathode active material according to Example 1 of the present invention has a superior composite density and carbon content compared to the cathode active material according to Comparative Example 1. It can be seen that the cathode active material according to Example 1 of the present invention has a smaller primary particle size compared to the cathode active material according to Comparative Example 1. It can also be seen that the cathode active material according to Example 2 of the present invention has a superior composite density and carbon content compared to the cathode active material according to Comparative Example 2. It can also be seen that the cathode active material according to Example 2 of the present invention has a smaller primary particle size compared to the cathode active material according to Comparative Example 2.

[0151] That is, it can be seen that when both the first and second particles are in the form of secondary particles, the composite density and carbon content are higher than when they are in the form of single particles, and the primary particles are smaller.

[0152] Evaluation Example 3: Active Material Evaluation II The composite density (PD) and carbon content of the positive electrode active materials of Examples 1, 2, 3-1 to 3-4 were measured, and the results are shown in Table 2.

[0153] [Table 2]

[0154] Referring to Table 2, it can be seen that Examples 3-2 to 3-4 of the present invention have similar mix densities to Example 1. It can be seen that Examples 3-3 to 3-4 of the present invention have similar carbon contents to Example 1. Overall, it can be seen that Examples 3-3 to 3-4 of the present invention have similar mix densities and carbon contents to Example 1.

[0155] Evaluation example 3: Battery characteristic evaluation The characteristics of the lithium secondary batteries manufactured using the positive electrode active materials of Comparative Examples 1 and 2 and Examples 1 to 3-4 were evaluated.

[0156] The lithium secondary battery was initially charged under constant current (0.2C) and constant voltage (4.45V) conditions, and after a 10-minute rest, discharged to 2.5V under constant current (0.2C) conditions to conduct the initial charge-discharge. It was then charged and discharged 50 times at 1.0C / 1.0C at 25°C. An additional coin cell was also fabricated and the 0.2C capacity was measured at -20°C.

[0157] The results of the battery characteristic evaluation are shown in Table 3 below.

[0158] [Table 3]

[0159] Referring to Table 3, it can be seen that the secondary batteries according to Examples 3-3 and 3-4 of the present invention have similar −20° C. capacities, average voltages, and life spans to those of Example 1.

[0160] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0161] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. First particles comprising a compound represented by Chemical Formula 1 below and having a first average particle size; and second particles comprising a compound of the following Chemical Formula 2 and having a second average particle size larger than the first average particle size, Each of the first particles and the second particles has a spherical secondary particle shape, A positive electrode active material, wherein the content of the first particles is equal to or greater than the content of the second particles: [Chemical formula 1] Li a1 Mn w1 Fe x1 Ti y1 B1 z1 PO 4-b1 In Chemical Formula 1, 0.8≦a1≦1.2, 0.3≦w1≦0.7, 0.3≦x1≦0.7, 0≦y1≦0.05, 0≦z1≦0.05, 0≦b1≦0.05, and x1+y1+z1+w1=1; [Chemical formula 2] Li a2 Fe x2 Ti y2 B2 z2 PO 4-b2 In Chemical Formula 2, 0.8≦a2≦1.2, 0.900≦x2≦0.999, 0.001≦y2≦0.05, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1; B1 in Formula 1 and B2 in Formula 2 each represent at least one element selected from the group consisting of transition metals having an oxidation number of 4.

2. The positive electrode active material of claim 1 , wherein the mixing ratio of the first particles to the second particles is in the range of 50:50 to 99:

1.

3. The first particles include a plurality of first primary particles that are aggregated together, the second particles include a plurality of second primary particles agglomerated together, The positive electrode active material of claim 1 , wherein the plurality of first primary particles have a size smaller than the plurality of second primary particles.

4. The positive electrode active material of claim 3 , wherein the first primary particles have a size of 50 nm to 200 nm.

5. The positive electrode active material of claim 3 , wherein the second primary particles have a size of 200 nm to 300 nm.

6. The positive electrode active material of claim 1 , wherein the Ti content of the first particles is greater than the Ti content of the second particles.

7. the Ti content of the first particles is 1,000 ppm to 3,000 ppm; The positive electrode active material of claim 6 , wherein the Ti content of the second particles is 1,000 ppm to 3,000 ppm.

8. 2 . The positive electrode active material of claim 1 , wherein a mixing ratio of the first particles and the second particles is such that a content of Mn relative to metal elements excluding lithium in the positive electrode active material is 25 at % to 70 at %.

9. the first average particle size is 1 μm to 7 μm; The positive electrode active material of claim 1 , wherein the second average particle size is 3 μm to 10 μm.

10. the first particles and the second particles include a first coating layer containing carbon; the carbon content in the first particles is 1.5 wt % to 2.0 wt %; The positive electrode active material of claim 1 , wherein the carbon content in the second particles is 1.0 wt % to 1.9 wt %.

11. The positive electrode active material of claim 1 , wherein the first particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

12. The positive electrode active material of claim 1 , wherein the second particles have a Span value of 0.3 to 0.75 as analyzed by a particle size analyzer.

13. The positive electrode active material of claim 1 , wherein the first particles have a porosity of 15% to 40%.

14. The positive electrode active material of claim 1 , wherein the second particles have a porosity of 15% to 30%.

15. Producing first particles having a first average particle size; producing second particles having a second average particle size; and mixing the first particles so that the content of the first particles is equal to or greater than the content of the second particles, Producing the first particles comprises: combining a manganese iron phosphate precursor, a first lithium source, a first carbon source, and a first titanium source to form a first mixture; drying the first mixture by spray drying; and calcining the dried first mixture; Producing the second particles comprises: combining an iron phosphate precursor, a second lithium source, a second carbon source, and a second titanium source to form a second mixture; drying the second mixture by spray drying; and calcining the dried second mixture.

16. 16. The method of claim 15, wherein a mixing ratio of the first particles to the second particles is in the range of 50:50 to 99:

1.

17. The method of claim 15 , wherein the Ti content of the first particles is greater than the Ti content of the second particles.

18. The spray drying agglomerating particles in the first mixture to form first secondary particles; agglomerating particles in the second mixture to form second secondary particles. The method for producing a positive electrode active material according to claim 15.

19. The first mixture and the second mixture used as the spray liquid for the spray drying are having a solids content of 20% to 40% by weight, The method for producing a positive electrode active material according to claim 15 , wherein the positive electrode active material has a viscosity of 1500 mPa·s to 2500 mPa·s.

20. A lithium secondary battery comprising the positive electrode active material according to claim 1.

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